Figure Dust-Collection Needs

Is it finally time to tackle the dust problem in your shop? Don't gamble by guessing on duct sizes and airflow. These basic calculations will tell you what flow capacity you need, what size ductwork that calls for, and how much static pressure loss your dust collector must overcome to work effectively.

You'll need to know the amount of air flowing in your system

Start by determining what the maximum airflow through the system will be. To do this, list the tools that you'll connect to the system. Beside each one, jot down the dust-collection air flow it requires in cubic feet per minute (CFM). You can come up with this figure several ways:

Look it up in the tool manual. (Not all manuals specify it.)

Use the typical airflow values shown in Table 1.

Figure the flow based on the size (thus, the flow capacity) of the tool's built-in dust-collection port. You can do this using one of these methods:

For a round port, measure the diameter. Then, select the corresponding CFM value from Table 2.

For a rectangular port, calculate the area (multiply length times width, in inches). Then, multiply that area times 28 to find the approximate flow in CFM @ 4,000 feet per minute (FPM).

The single largest CFM figure on your list represents the maximum airflow your dust-collection system will have to support. (This assume that airflow from each machine can be shut off with a blast gate. If you will have more than one machine operating at once or if a single blast gate serves more than one machine, add together the figures for those machines to find the maximum flow.) Enter this CFM figure on Worksheet 1.

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